JP3012017B2 - Automatic gain control method for radiation measurement device and automatic gain control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation measuring apparatus used for measuring the density of a sample to be measured and, more particularly, to automatically controlling a detection gain so as to perform measurement in an optimum dynamic range. On how to do it.

[0002]

2. Description of the Related Art Heretofore, a gamma ray density measuring device has been known as a radiation measuring device for measuring the density of a sample to be measured.
The structure of a conventional γ-ray density measuring device will be described with reference to FIG. 6. This device is used, for example, for laying pavement asphalt in road pavement work and then measuring the density of the pavement asphalt to check the construction status. Used for etc. Then, a radiation source 1 that emits a gamma ray pulse to a sample to be measured such as asphalt for pavement, and a detector 2 such as a scintillation counter that detects a gamma ray pulse that has passed through the sample to be measured are included in the measuring device. Provided in the housing,
Further, a calculation unit 3 is provided for calculating the density ρ of the sample to be measured by calculating the pulse train detected by the detector 2.

The detection signal detected by the detector 2 is first input to a pulse amplifier 4 of an arithmetic unit 3, amplified and shaped, and supplied to a multi-window comparator 5. The multi-window comparator 5 includes a plurality of level detection circuits, and discriminates which signal level each waveform-shaped signal belongs to. Then, the processing unit 6 counts the number of pulses in each signal level range per unit time determined in advance, and supplies data of the counted value to a CRT display or the like at a cycle of unit time.
Processing such as displaying a pulse height diagram indicating each count value for each signal level range is performed.

Therefore, if the signal detected by the detector 2 has a distribution as shown in FIG. 7 per unit time τ, the multi-window comparator 5
Determines the energy level of each signal in a signal level range corresponding to a plurality of energies obtained by dividing the signal level range corresponding to the maximum measurable energy into several ranges. , The pulse height diagram of the energy versus the count value is formed as shown in FIG. And the processing unit 6
The density ρ of the sample is calculated from the correlation curve data of the count value and the sample density set in advance.

The processor 6 automatically adjusts the output voltage of the variable voltage source 8 for supplying control power to the detector 2 in order to operate the detector 2 with an optimum dynamic range. This automatic adjustment is performed by the multi-window comparator 5
The processing unit 6 analyzes the transferred data for counting and determines whether or not the data is in an optimum state.
The conversion is performed by converting the voltage into an analog signal by the / A converter 7 and adjusting the output voltage of the variable voltage source 8 according to the level of the analog signal.

That is, the detector 2 has a characteristic that the gain changes when the voltage supplied from the variable voltage source 8 changes. For example, as the voltage decreases, the gain decreases, and conversely, as the voltage increases, the gain increases. In order to automatically adjust the gain of the detector 2 so that the relationship between the input signal level and the scattered γ-ray energy always has a predetermined relationship, for example, in the pulse height diagram of FIG. The signal level set in the multi-window comparator 5 (corresponding to the optimum dynamic range).
This is realized by controlling so as to match EM (hereinafter, referred to as a static settling signal level). FIG. 8 shows a case where measurement is performed at the optimum gain. When measurement is performed with such a radiation measuring instrument, the detector 2 has a high energy peak P1 corresponding to the decay energy of the radiation source 1, Since a low-frequency energy distribution P2 of the scattered γ-ray pulse appears by scattering in the sample, the control voltage to the detector 2 is automatically adjusted so that the peak P1 coincides with the above-mentioned static signal level EM. This sets the optimal dynamic range.

Further, the conventional operation principle for performing the optimum processing by determining whether the peak P1 and the static signal level EM coincide with each other will be specifically described. FIG. 9 is a pulse height diagram of the signal level versus the count value when the optimum measurement state is set. In order to automatically adjust to this state, a preset value on both sides centering on the static signal level EM is set. Specified signal level ranges (windows) W1, W
The output voltage of the variable voltage source 8 is controlled so that the count values # 1 and # 2 in Eq. If the gain of the detector 2 is high, the high energy peak P1 moves to a position higher than the static signal level EM as shown in FIG. 10, so that the count value Σ1 becomes larger than the count value Σ2. The processing unit 6 discriminates the magnitude relationship and lowers the output voltage of the variable voltage source 8 to control the position of the peak value P1 in FIG. 10 to move in the direction of the static set signal level EM.

On the other hand, when the gain of the detector is low, FIG.
Since the position of the high-energy count value P1 is lower than the static set signal level EM, the count value よ り 1 is smaller than the count value 、 2, and the processing unit 6 discriminates and changes the value. The output voltage of the voltage source 8 is increased and the detector 2
The peak P shown in FIG.
1 is moved in the direction of the static signal level EM.

As described above, in the conventional radiation measuring apparatus, the peak P1 corresponding to the decay energy of the radiation source detected by the detector has a predetermined static signal level EM.
The optimum dynamic range was obtained by automatically performing feedback control of the control voltage to the detector so as to coincide with the above.

[0010]

However, in such a conventional automatic gain control method, as shown in FIG. 12, the peak P1 on the high energy side has a static set signal level EM.
If the position deviates significantly from the position, the position may deviate from the lockable state, and automatic control may be difficult.
That is, in the conventional method, the count value # 1 shown in FIGS.
Although the presence or absence of the optimum state is determined from the difference between Σ and Σ2, only feedback control is performed so as to make this difference zero, and it is not determined how much the peak P1 is from the static set signal level EM. The direct adjustment of the gain of the detector 2 has not been performed. Therefore, it takes a long time to stabilize to the optimum dynamic range. Further, as shown in FIG. 12, if it is out of the lockable state, automatic adjustment is extremely difficult, and manual operation must be performed. Was complicated.

The present invention has been made in view of such a conventional problem, and has as its object to provide an automatic gain control method in which an optimum dynamic range is set at a high speed and with high accuracy.

[0012]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a radiation source for emitting radiation to a sample to be measured, and a detection source for detecting radiation passing through the sample to be measured. Means, and counting means for counting the number of detection signals for each signal level corresponding to each of a plurality of levels of energy in the detection signal output from the detection means, and the signal level versus the count value obtained by the counting means. Automatic gain control method for a radiation measuring apparatus for automatically controlling the gain of the detection means so that the statically determined signal level of the decay energy set in advance from the signal coincides with the signal level corresponding to the decay energy of the incident radiation source. And an automatic gain control device.

Then, when the control voltage for controlling the gain of the detecting means is sequentially changed from the lowest voltage to the highest voltage, discrimination is made for each of a plurality of windows corresponding to a plurality of energy level ranges at each voltage. The magnitude relation of the count values of the signals to be stored is stored, and the detection means detects the radiation. Based on the magnitude relation of the count values of the signals discriminated for each window and the magnitude relation stored above, An error of the gain from the control voltage is determined, and a gain control corresponding to the error is performed on the detecting means.

[0014]

According to the automatic gain control means of the present invention, the deviation from the optimum applied voltage to be applied to the detection means is determined from the magnitude relation of the count values of the signals discriminated for each window. The gain control corresponding to the error can be directly performed on the detection means. As a result, the stabilization control for operating the detection means at the optimum gain can be performed at a higher speed than in the past.

[0015]

An embodiment of the present invention will be described below with reference to the drawings. First, the configuration of an embodiment of a γ-ray density measuring apparatus to which the method of the present invention is applied will be described with reference to FIG. In the figure,
1 is a radiation source, 2 is a scintillation detector for detecting a γ-ray pulse emitted from the radiation source 1 and passed through the sample to be measured, and an area 3 within a dotted line is an arithmetic unit. Further, reference numeral 4 denotes a pulse amplifier for amplifying the signal output from the detector 2 and performing pulse width shaping, and 5 denotes a signal level corresponding to the energy of each pulse signal output from the pulse amplifier 4 for a predetermined unit time. A multi-window comparator 6 for determining the number of signals at each signal level corresponding to each energy discriminated by the multi-window comparator 5 and determining the number of signals at each signal level from the data of the count value; Processing such as calculating the density ρ based on a predetermined correlation curve is performed.

Further, the processing unit 6 automatically adjusts the output voltage of the variable voltage source 8 for supplying electric power to the detector 2 in order to operate the detector 2 with the optimum dynamic range.
In this automatic adjustment, the processing unit 6 analyzes data for counting transferred from the multi-window comparator 5 to determine whether or not the data is in an optimum state, and outputs data indicating the adjustment amount to D / A.
The conversion is performed by converting into an analog signal by the converter 7 and adjusting the output voltage of the variable voltage source 8 according to the level of the analog signal.

Reference numeral 9 denotes a look-up table constituted by a ROM (read-only memory) or the like, in which data of an adjustment amount corresponding to a result analyzed by the processing section 6 is stored in advance.
The processing unit 6 reads out the data of the adjustment amount corresponding to the analysis result and supplies the data to the D / A converter 7 so that the variable voltage source 8
Is changed according to the data of the adjustment amount.

The multi-window comparator 5 has, for example, the configuration shown in FIG. That is, a signal that has been subjected to processing such as waveform shaping by the pulse amplifier 4 is supplied to one input contact of a plurality of comparators CW1 to CW5 via a buffer amplifier, and the other input contact of these comparators CW1 to CW5. Are set to predetermined different reference potentials via ladder resistors. The outputs of the comparators CW1 to CW5 are connected to the input contacts of the latch circuit 10. The pulse amplifier 4 generates a reset signal RS in synchronization with the timing at which the signal from the detector 2 is applied, and the latch circuit 10 transfers internal data to the decoder 11 and Since the state is reset, new data from the comparators CW1 to CW5 are sequentially latched and transferred in synchronization with the timing at which the detection signal is supplied.

The decoder 11 converts the data of the latch circuit 10 into data of a predetermined format and stores the data in a memory 12 such as a FIFO memory one by one. Then, the data in the memory 12 is supplied to the processing unit 6. Here, the comparators CW1 to CW5
Are set in order to appropriately divide the signal level range corresponding to the measurable energy. For example, in the pulse height diagram shown in FIG. 9, the reference potential set in the comparator CW1 discriminates the signal of the level corresponding to the window W1, and the comparator CW2
The reference potential set in the comparator CW3 discriminates the signal of the level corresponding to the window W2, and the reference potential set in the comparator CW3 discriminates the signal of the level corresponding to the window W3. The reference potential present discriminates the signal of the level corresponding to the window W4, and the comparator CW
The reference potential set to 5 is set so as to discriminate the signal of the level corresponding to the window W5.

Next, an automatic adjusting function of the apparatus having the above-described configuration will be described. First, the relationship between the magnitude of the count value of the signal discriminated for each window and the control voltage of the variable voltage source 8 will be described. The output voltage of the variable voltage source 8 is set to the minimum voltage (minimum voltage for enabling the detector 2 to perform the measurement operation) Vm
To the maximum voltage (maximum voltage for enabling the detector 2 to perform the measurement operation) VM, and the detection unit 2 detects the radiation with each applied voltage, and the respective windows W1 to W1 of the multi-window comparator 5 When counting the number of each signal corresponding to W5, the variable voltage source 8 as shown in FIG.
Is obtained. The curve W1 in FIG. 3 shows the distribution of the count value of the signal detected by the comparator CW1, the curve W2 similarly shows the distribution of the count value of the signal detected by the comparator CW2, and the curve W3 shows the distribution of the count value. The distribution of the count value of the signal detected by CW3, the curve W4 is the distribution of the count value of the signal detected by the comparator CW4, and the curve W5 is the distribution of the count value of the signal detected by the comparator CW5. Distribution W1
The maximum value of ~ W5 is normalized as 1.

The voltage V0 in FIG. 3 is the output voltage of the variable voltage source 8 when the peak corresponding to the decay energy of the radiation source 1 is in an optimum state that matches the static signal level EM (see FIG. 9). It is. As is clear from FIG. 3, the normalized values of the respective windows W1 to W5 have a unique magnitude relationship according to the output voltage of the variable voltage source 8. Therefore,
When the actual measurement is performed, the processing unit 6 sets the windows W1 to W1.
By comparing the magnitude relations of the count values for each W5, it is determined whether the gain of the detection unit 2 is high, that is, FIG.
As shown in FIG. 1, it is determined whether or not the peak corresponding to the decay energy of the radiation source 1 does not match the static signal level EM.

First, in FIG. 3, the normalized value of the range of the window W1 is n1, the normalized value of the range of the window W2 is n2, the normalized value of the range of the window W3 is n3, and the normalized value of the range of the window W4. Is n4 and the normalized value of the range of the window W5 is n5, the output voltage (hereinafter, control voltage) V of the variable voltage source 8 is in the range of Vm ≦ V ≦ V1. When the magnitude relationship is determined, the relationship of n5>n4>n3>n2> n1 is established.

Similarly, for voltages in the range of V1 <V ≦ V2, the relationship of n4>n5>n2>n1> n3 holds. Further, for voltages in the range of V2 <V ≦ V3, the relationship of n4>n2>n5>n1> n3 is established, and the magnitude relationship is also uniquely established for other voltage ranges.

Therefore, by using these magnitude relations, it is possible to specifically determine how many volts are different between the control voltage V for setting the optimum dynamic range and the current control voltage. That is, in the lookup table 9, as shown in FIG. 4, for example, data of the voltage to be changed is stored in advance corresponding to each magnitude relationship, and the processing unit 6 corresponds to the determination result of the magnitude relationship. The data is read and supplied to the variable voltage source 8.

Here, the data of the voltage to be changed is determined by the following method. That is, a deviation between the intermediate voltage in the range of the control voltage V that can be determined based on the magnitude relation and the optimum voltage V0 is set. For example, as shown in FIG. 4, n5>n4>n2> n
The control voltage V in the relationship of 1> n3 is Vm ≦ V ≦
Since the voltage is specified in the range of V1, the intermediate voltage is (Vm
+ V1) / 2, and the voltage to be changed is V0− (Vm + V
1) / 2.

Although there is an error in the value of the intermediate voltage, a control voltage close to the optimum state can be initially set, so that sufficient control for escaping from the conventional lock disabled state is achieved. That is, after the control at the initial stage is completed, the gain control described in the related art can be performed to perform high-speed voltage adjustment. Further, the look-up table 9 as shown in FIGS. 3 and 4 and the normalized value for each voltage can be obtained by performing one measurement in advance. Even if the absolute value of the control voltage changes due to the aging of the external environment in the actual measurement after that,
Since the relative value (normalized value) does not change so much, once it is set, the data of the lookup table 9 as shown in FIG. 4 can be continuously used.

Next, a control method according to another embodiment will be described with reference to FIG. Note that the configuration when the device is implemented is the same as that shown in FIGS. In this embodiment, instead of performing the normalization processing with the maximum value for each window as shown in FIG. 3 in the description of the first embodiment, the count value for each window is divided by a predetermined constant k. are doing. Therefore, although the respective division results may exceed 1, the magnitude relationship can be determined in the same manner as in the first embodiment. In particular, by setting the constant k to a value corresponding to the characteristic characteristic of the radiation measuring apparatus, for example, control suitable for different types of apparatuses can be performed.

When the control voltage can be uniquely obtained from the magnitude relation of the count value for each window, k =
The division may be set to 1 to omit the division process. In these embodiments described above, the case where the magnitude relationship of the count value (normalized value) between the windows is determined for all the windows has been described. However, the present invention is not limited to this. May be determined, and the voltage to be changed may be determined based on this.

Although the case where the scintillation counter is applied as the detector has been described, the present invention is not limited to this, and the gain control means of the present invention can be applied to the case where other types of radiation sources are applied.

[0030]

As described above, according to the present invention, a plurality of control voltages for operating the detecting means for detecting radiation are sequentially changed from the lowest voltage to the highest voltage. The magnitude relation of the count value of the signal discriminated for each of a plurality of windows corresponding to the energy level range is stored, and the detection means detects radiation at each voltage, and the count value of the signal discriminated for each window. An error from the control voltage of the optimal gain is determined based on the magnitude relationship of the above and the magnitude relationship stored above, and the gain control corresponding to the error is performed on the detection means, so that each window is controlled. The deviation from the optimum applied voltage for applying to the detecting means can be determined from the magnitude relationship of the count values of the signals discriminated every time, and the deviation corresponding to this error can be determined. It can be carried out directly on the detector and the resulting control. As a result, the stabilization control for operating the detection means at the optimum gain can be performed at a higher speed than in the past.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a radiation measuring apparatus to which the present invention is applied.

FIG. 2 is a circuit diagram showing a configuration of a multi-window comparator in FIG.

FIG. 3 is an explanatory diagram for explaining an operation and effect of the gain control according to the embodiment;

FIG. 4 is another explanatory diagram for explaining the function and effect of the gain control according to the embodiment;

FIG. 5 is an explanatory diagram for explaining an operation and effect of gain control of another embodiment.

FIG. 6 is a block diagram showing a configuration of a conventional radiation measurement device.

7 is a diagram showing the radiation detection signals shown in FIG. 6 in chronological order.

FIG. 8 is a diagram showing a pulse height diagram corresponding to the detection result of FIG. 7;

FIG. 9 is an explanatory diagram for explaining the principle of conventional gain control with a pulse height diagram.

FIG. 10 is an explanatory diagram for further explaining the principle of conventional gain control with a pulse height diagram.

FIG. 11 is an explanatory diagram for further explaining the principle of conventional gain control with a pulse height diagram.

FIG. 12 is an explanatory diagram for explaining a problem of the conventional gain control with a pulse height diagram.

[Explanation of symbols]

 2; detector 4: pulse amplifier 5; multi-window comparator 6; processing unit 7; D / A converter 8; variable voltage source 9; look-up table 10; latch circuit 11; decoder 12;

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 9/24

Claims (2)

(57) [Claims] 1. A radiation source for emitting radiation to a sample to be measured, a detecting means for detecting radiation passing through the sample to be measured, and a detection signal output from the detecting means in each of a plurality of stages. Counting means for counting the number of detection signals for each signal level corresponding to energy, and a predetermined statically-determined signal level of decay energy is input from the signal level versus the count value obtained by the counting means. In the automatic gain control method of the radiation measuring device for automatically controlling the gain of the detection means so as to match the signal level corresponding to the decay energy of the coming radiation source, a control voltage for controlling the gain of the detection means is set in advance. , Signals that are discriminated by a plurality of windows corresponding to a plurality of energy level ranges at each voltage when sequentially changed from the lowest voltage to the highest voltage. The magnitude relation between the count values of the signals is stored in advance, and the detection means detects the radiation. Based on the magnitude relation between the count values of the signals discriminated for each window and the magnitude relation stored as described above, the optimum gain of the optimum gain is determined. An automatic gain control method for a radiation measuring apparatus, comprising: determining an error from a control voltage, and performing gain control corresponding to the error to a detection unit. 2. A radiation source for emitting radiation to a sample to be measured, detecting means for detecting radiation passing through the sample to be measured, and a plurality of stages of detection signals output from the detecting means. Counting means for counting the number of detection signals for each signal level corresponding to energy, and a predetermined statically-determined signal level of decay energy is input from the signal level versus the count value obtained by the counting means. In the automatic gain control device of the radiation measuring device for automatically controlling the gain of the detection means so as to match the signal level corresponding to the decay energy of the coming radiation source, a control voltage for controlling the gain of the detection means is set in advance. , Signals that are discriminated by a plurality of windows corresponding to a plurality of energy level ranges at each voltage when sequentially changed from the lowest voltage to the highest voltage. Storage means for storing the magnitude relation between the count values of the signals, and detecting means for detecting radiation, and determining the optimum gain based on the magnitude relation between the count values of the signals discriminated for each window and the magnitude relation of the storage means. An automatic gain control device for a radiation measuring apparatus, comprising: a control unit that determines an error from the control voltage of the control unit and performs gain control corresponding to the error to a detection unit.